Uranus

Probably the least famous planet in our Solar System, Uranus is without doubts one of the most exceptional and unique worlds. Flipped on one side as a result of a massive collision, this cyan-tinted world hides unexpected wonders and unique features: extreme seasons, astonishing rings and…orbiting moons named after Shakespeare’s characters!

Observed since ancient times, with first observations tracing back to Hipparchos (128 BC), Uranus was the first planet to be recognised as such with the aid of a telescope. For centuries, in fact, the planet had been mistaken for a star before Sir William Herschel pointed his homemade 7-foot telescope at it, in 1781.

And even then, he thought he was glancing at a comet. It was only after few years that the object was universally accepted as another planet orbiting the Sun. The discovery gained Herschel the official protection of King George and the astronomer, to express his gratitude, proposed to name the planet after the King. Finally, the recent discovery of a new metal (Uranium) led the scientific community to accept another of the proposed names: Uranus, the Greek god of the sky.

Uranus is the seventh planet from the Sun at 2.9 billion km and has the third-largest diameter and the fourth-largest mass in the Solar System. Compared to Earth, it is 4 times wider: by comparison, if our planet were a tennis ball, Uranus would be a basketball.

But size is not what makes it unique and bizarre. Possibly the result of a massive collision, Uranus’ axis is tilted about 98 degrees (Earth’s tilt is 23.5) meaning it appears flipped on one side, with one of its poles pointing toward the Sun. It is the only planet in the Solar System spinning almost on its side!

Another peculiarity of this Ice Giant is that, along Venus, it is the only planet in the Solar System to rotate counterclockwise, with the Sun rising in the west. A day on Uranus is relatively short at 17 hours whereas a year, the time Uranus takes to make a complete orbit around the Sun, takes around 84 Earth years, a full human life.

And that is not all. The extreme tilt of the axis also contributes to the planet’s weird seasons with the northern hemisphere experiencing 21 years of continued day light in summer, 21 of years of dark in winter and 21 years of equally split daylight and night-time in the spring and fall.

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Together with Neptune, Uranus is usually classified as “Ice Giant”. The “Ice” refers to the composition of the mass that contains a hot dense fluid of water, ammonia and methane, which planetary scientists tend to call “ices”, for they solidify at cold temperatures. And never mind the fact that inside the atmosphere these ices boil under the extreme pressure. They still classify as “ices”.

The atmosphere is mostly hydrogen and helium, but it is methane that confers Uranus its distinctive pale blue colour. As seen in other giant planets, the upper atmosphere experiences extreme storms with winds up to 900 km per hour in the direction of rotation. The planetary temperature is the coldest in the Solar System with peaks at -224 °C.

Like Saturn, Uranus has its own systems of rings: 13 ultra-thin hoops of tightly packed icy rocks and dust that encircle the planet vertically rather than horizontally, due to the extreme tilt of the planet’s axis.

Uranus has also 27 known moons in its orbit, largely composed of ice water and rock. They are named after the characters from the works of William Shakespeare and Alexander Pope: from Juliet and Ophelia to Ariel and Umbriel, Uranus is certainly in good company.